Multiple sclerosis is a disease in which the protective myelin coat of nerve cells in the brain and spinal cord become damaged. Consequently, any function related to the central nervous system can be adversely affected, but the most common symptoms are severe fatigue, visual problems, altered sensitivity, and reduced mobility. The root cause of multiple sclerosis is still unknown, but the research community has learned that it is an abnormal immune-mediated response that attacks the myelin coating.